Defrosting and frost prevention



Feb; 2 1944- M s. scl-lEcHTEk ETAL 2, v DEFROSTING AND FROST PREVENTION Original Filed Aug. 51, 1940 4 Z z s a) 7 I I S sc HEcHT g l I Patented Feb. 29, 1944 Milton S. Schechter and Herbert L. J. Ballet, Washington, D. 0.

Original application August 31, 1940:. Serial No.

4 Claims.

This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described and claimed, if patented, may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to us of any royalty there- This is a division of our copending application for; patent, Serial No. 354,949, filed August 3 19 0. I

This invention has for its chief object the provision of a method for eliminating frost and ice formations on the cooling or heat exchange unlts'of refrigerating systems. Another object of this invention i the provision of a method for defrosting the cooling units of refrigerating systems-and for maintaining them free of frost and ice during the operation of the refrigerator without shutting off the refrigerating machinery. Other objects will be apparent from the description hereafter given.

"Frost as used in this description includes I Frost being a relatively poor conductor of heat,

the transfer of heat between the surrounding atmosphere and the heat exchange. unit is greatly hindered by the frost and consequently the efficiency of refrigeration is significantly W-'. ered. Inaorder to compensate for a poor transfer of heat through the frost, the heat exchange unit must be kept at a temperature lower than what would otherwise be necessary if such frost were not present, thus putting a heavier load on the refrigerating machinery. Furthermore, the building up of layers of frost on heat exchange units necessitates some method of defrosting the units from time to time, which is Divided and this application July 17, 1943, Serial No. 495,204

(Granted under the act of March a, 1m, .5 amended April 30, 1928; 370 0. G. 757) freezing point of a liquid when dissolved .in it.

both expensive and time-consuming. Some of for such a length of time that the heat exchange unit can warm up sufficiently to permit the frost to melt.

2. Removing'the frost from the cooling unit by mechanical means, such as chopping, scraping, and so forth. 1

3. Attempting to prevent frost formation on the cooling unit by the use of special paints.

Besides being both time-consuming and expensive, none of these methods has been found in whole or in part in proximity to the cooling or heat exchange unit. The liquid should be volatile enough to distill fromthe container to the cooling unitunder the small temperature differential prevailing between the unit and the surrounding air. Some of the liquids which have been found to work well in the process are methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, "acetone, methyl ethyl ketone and diethyl ketone. Mixtures of liquids can also be used. The foregoing examples are merely illustrative of the liquids which may be used in the process, and this invention is not to be considered' limited thereby. is not limited to the use of alcohols or ketones or mixtures thereof, for although these types of compounds have been found \to work most satisfactorily, other classes of compounds may also be used.

Our novel process depends for its success on the fact that a compound will distill from a warmer region to a cooler region. It also de- Thus, in the defrosting process. the volatile liquid distills from the container tothe cooling unit because of the difference in temperature between the two, even though the difference is slight. Upon coming into contact with the frost on the cooling unit, the condensed liquidcauses the frost to melt, due to the lowering of the freezing point of the frost by the presence of the liquid which has distilled. The condensed liquid, together with the melted frost, then falls oil the cooling unit. (The process of defrostin is believed to take place as outlined above. However, this invention is not to be considered limited in any manner by the explanation offered.)

If the vessel containing the volatile liquid used in the process is placed beneath the. cooling unit Also, this invention one. One vessel may be used to catch the drip pings, while the other vessel, with the-volatile so-as to receive from it the melted frost plus condensed volatile liquid from the cooling unit, the volatile liquid in the container will progressively become more and more dilute until it finally loses its full effectiveness. We have innovated modifications of our process which greatly minimize this dilution effect.

One modification of our process comprises placing in' the vessel, in addition to the volatile liquid, a water-soluble compound or.material capable of salting out the volatile liquid from an aqueous solution thereof. Water-soluble compounds suitable for use in this modification of the process are sodium chloride, sodium carbonate, sodium sulfate, sodium dihydrogen phosphate, disodium phosphate,'potassium chloride, potassium carbonate, potassium sulfate, potassium dihydrogen phosphate and dipota'ssium phosphate. These compounds .are cited merely by way of illustration and not by way of limitation, since any water-soluble compound capable of establishing a salting out effect on the liquid used in theprocess may be employed. The function of the compound so used is to cause a separation of the mixture in the container into two phases, namely, alower phase consisting essentially of v an aqueous solution of the compound and an up-' 'per phase consisting essentially of the volatile,

liquid. The volatile liquid is thus kept floating as the upper phase and is maintainedpractically undiluted by the melted frost from the cooling unit. Consequently. it is available for continued use in the process. The lower phase can be drawn off whenever necessary anddiscarded or, if desired, the compound dissolved therein, may be recovered and returned to the system by evaporating the water.

An'other modification of our process comprises placing in the vessel, in addition to the volatile liquid, a compound or material which will dehydrate, in whole or in part, the liquid used in the, process. Compounds or materials suitable for use in this modification are anhydrous sodium carbonate, anhydroussodium sulfate, anhydrous potassium carbonate, anhydrous magnesium sulfate, anhydrous calcium sulfate, calcium chloride, calcium oxide, barium oxide, anhydrous copper sulfate, and activated aluminum oxide. These compounds are cited merely by way of illustration and not by limitation and it is to be understood that this invention is not limited thereby. Any drying agent capable of dehydrating or removing water in whole or in part from the volatile liquid used may be employed. The function of the dehydrating agent is to maintain the volatile liquid in a dry or reasonably dry state, so that the liquid does not become diluted with too much water.

Certain drying agents can be reactivated by removing absorbed water.

This invention can be varied in manyQways. For example, two vessels may be used instead of liquid, is placed at some other point in the refrigerator. The first vessel, if .desired, may contain a compound capable of effecting a salting out reaction or it may contain a compound or mate rial having dehydrating or drying properties in order to remove water from the drippings, but

' the use of such compounds is not indispensable,

time.

since the full strength of the volatile liquid will be retained in the second vessel. Where such modifications are employed, a drain pipe from the lower phase in the first vessel to the exterior of the refrigerator .housing may be employed, so that this phase may be drawn off from time to tween the upper phase of the first vessel and the second vessel, so that salted out or dehydrated volatile liquid in the first container may be returned to the second vessel, thereby making the system regenerative with respect to the volatile liquid.

vessel 4 containing the volatile liquid.

Where this is possible the drying agent may be used over and over again.

In the accompanying drawing, there is illustrated the modification-of our invention in which two vessels are employed. The drawing is a vertical section of a refrigerator box i containing the usual cooling coils or heat exchange unit 2; Below the unit 2, there is disposed a vessel 3 for catching the drippings from the unit 2, At another point in the box, there is disposed another In the drawing. this vessel 4 is placed directly beneath the vessel 3. However, any point in the refrig-' erator is suitable so long as the vessel 4 is kept free from dilution. The vessel 3 is provided with either a salting out or a dehydrating compound for the purposes mentioned above, and an overflow 5 from the vessel 3 to the vessel 4 is provided. Also, a drain pipe 6 having a valve 1 is connected to the vessel 3 to draw off, occasionally, excess quantities of the lower phase.

Having thus described our invention, we claim:

1. In combination with a refrigeration system having an evaporator unit, a vessel-beneath said unit in a region normally warmer than the evaporator to catch drippings therefrom, said vessel containing a volatile water-miscible liquid and a compound capable of salting out the volatile liquid from aqueous solutions thereof.

2. In combination with a refrigeration system having an evaporator unit, a vesselabeneath said unit in a region normally warmer than the evaporator to catch drippings therefrom, said vessel containing a volatile water-miscible liquid and a compound chosen from the group consisting of sodium chloride, sodium carbonate, sodium sulfate, sodium dihydrogen phosphate, disodium phosphate, potassium chloride, potassium carbonate, potassium sulfate. potassium dihydrogen phosphate.and dipctassium phosphate.

3. In combination with a refrigeration system having an evaporator unit, a vessel beneath said unit in a region normally warmer than the evaporator to. catch drippings therefrom, 'said vessel containing a volatile water-miscible liquid and a dehydrating agent.

4. In combination with a refrigeration system having an evaporator unit, a vessel beneath said unit in a region normally warmer than the evaporator to catch drippings therefrom, said vessel containing a volatile water-miscible liquid and a I dehydrating agent chosen from the group consisting of anhydrous sodium carbonate, anhydrous sodium sulfate, anhydrous potassium carbonate,

anhydrous magnesium sulfate, anhydrous calcium sulfate, *calcium chloride, calcium oxide. barium oxide, anhydrous copper sulfate and activated aluminum oxide. MILTON 8. SCHECHTER. HERBERT L. J. HAILER.

Also, a pipe connection may be used be- 

